Semiconductor memory device for use in an electrically alterable read-only memory

Abstract

This disclosure relates to an electrically alterable memory device which can be switched from a high resistance state to a low resistance state. The device increases the concentration of electrically active impurities at correspondent electrode to which respective impurities would migrate during a large number of set-reset cycles. This lessens the decline in the threshold voltage caused by the electromigration of those impurities. The device includes a layered structure in which a layer rich in electrically active impurities is placed between memory material layer and its respective electrode and another layer. A fitted thin layer of dielectric is placed between a memory material layer and the other electrode. The memory layer includes an interface of chalcogenide films. A tellurium layer with a concentration of electrically active impurity 2.5%-4.5% is placed between the memory layer and one of the electrodes while a germanium and tellurium or stanus and tellurium layer, with approximate percentage 1:1 and containing an intermediate layer of dielectric having fitted negative charge not less than 10 19 sm -3 , is placed between the memory layer and the other electrode.

I claim: 
     
       1. An electrically alterable memory device comprising: a lower electrode;   an upper electrode; and   a layer structure mounted inbetween said electrodes, which structure is constructed of first, second and third regions, said first region being adjacent to said lower electrode, said third region being adjacent to said upper electrode, said second region being between said first and third regions;   said second region being formed by the mutual diffusion of the main constituents of the first and third regions in order to provide a higher electrical resistance in one metastable state and lower electrical resistance in other metastable state, with switching from one state to the other upon application to the electrodes of an electrical signal of appropriate polarity, amplitude and duration;   said first region being formed of a material based tellurium with an electrically active donor impurity;   said third region being formed of a material having approximately equal percentages of tellurium and germanium or tellurium and stanus and containing inside an intermediate thin film of dielectric with a quantity of a fitted negative charge; and   said second region being formed because of a mutual diffusion of the main constituents of said first and third regions and have a higher percentage of tellurium than said third region.   
     
     
       2. A memory device according to claim 1 wherein said first region is formed of a material based tellurium containing from 2.5% to 4.5% of electrically active donor impurity. 
     
     
       3. A memory device according to claim 1 wherein the intermediate thin layer of dielectric in the third region has a quantity of a fitted negative charge not less than 10 19  sm -3 . 
     
     
       4. A memory device according to claim 1 wherein said second region is formed of Ge 32  Te 64  Al 4 . 
     
     
       5. A memory device according to claim 1 wherein said second region is formed of Sn 32  Te 64  Al 4 . 
     
     
       6. An electrically alterable memory device comprising: a lower electrode;   an upper electrode; and   a layer structure mounted inbetween said electrodes, which structure is constructed of first, second and third regions, said first region being adjacent to said lower electrode, said third region being adjacent to said upper electrode, said second region being between said first and third regions;   said second region being formed by the mutual diffusion of the main constituents of the first and third regions in order to provide a higher electrical resistance in one metastable state and lower electrical resistance in other metastable state, with switching from one state to the other upon application to the electrodes of an electrical signal of appropriate polarity, amplitude and duration;   said first region being formed of a material based tellurium with an electrically active donor impurity in close proximity thereto;   said third region being formed of a material having approximately equal percentages of tellurium and germanium or tellurium and stanus and containing inside an intermediate thin film of dielectric with a quantity of a fitted negative charge; and   said second region being formed because of a mutual diffusion of the main constituents of said first and third regions and have a higher percentage of tellurium than said third region.   
     
     
       7. The memory device according to claim 6 wherein the electrically active donor being included in the lower electrode which is adjacent said first region. 
     
     
       8. A memory device according to claim 6 wherein the electrode contains from 2.5% to 4.5% of electrically active donor impurity. 
     
     
       9. A memory device according to claim 6 wherein the intermediate thin layer of dielectric in the third region has with a quantity of a fitted negative charge not less than 10 19  sm -3 . 
     
     
       10. A memory device according to claim 6 wherein said second region is formed of Ge 32  Te 64  Al 4 . 
     
     
       11. A memory device according to claim 1 wherein said second region is formed of Sn 32  Te 64  Al 4 . 
     
     
       12. An electrically alterable memory device comprising: a lower electrode;   an upper electrode; and   a layer structure mounted inbetween said electrodes, which structure is constructed of first, second and third regions, said first region being adjacent to said lower electrode, said third region being adjacent to said upper electrode, said second region being between said first and third regions;   said second region being formed by the mutual diffusion of the main constituents of the first and third regions in order to provide a higher electrical resistance in one metastable state and lower electrical resistance in other metastable state, with switching from one state to the other upon application to the electrodes of an electrical signal of appropriate polarity, amplitude and duration;   said first region being formed of a material based tellurium and activated by a 2.5% to 4.5% of electrically active donor impurity;   said third region being formed of a material having approximately equal percentages of tellurium and germanium or tellurium and stanus and containing inside an intermediate thin film of dielectric with a quantity of a fitted negative charge; and said second region being formed as the result of a mutual diffusion of the main constituents of the first and third regions and having a higher percentage of tellurium than said third region.